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'use strict';
const common = require('../common');
// Ensure that subscribing the 'data' event will not make the stream flow.
// The 'data' event will require calling read() by hand.
//
// The test is written for the (somewhat rare) highWaterMark: 0 streams to
// specifically catch any regressions that might occur with these streams.
const assert = require('assert');
const { Readable } = require('stream');
const streamData = [ 'a', null ];
// Track the calls so we can assert their order later.
const calls = [];
const r = new Readable({
read: common.mustCall(() => {
calls.push('_read:' + streamData[0]);
process.nextTick(() => {
calls.push('push:' + streamData[0]);
r.push(streamData.shift());
});
}, streamData.length),
highWaterMark: 0,
// Object mode is used here just for testing convenience. It really
// shouldn't affect the order of events. Just the data and its format.
objectMode: true,
});
assert.strictEqual(r.readableFlowing, null);
r.on('readable', common.mustCall(() => {
calls.push('readable');
}, 2));
assert.strictEqual(r.readableFlowing, false);
r.on('data', common.mustCall((data) => {
calls.push('data:' + data);
}, 1));
r.on('end', common.mustCall(() => {
calls.push('end');
}));
assert.strictEqual(r.readableFlowing, false);
// The stream emits the events asynchronously but that's not guaranteed to
// happen on the next tick (especially since the _read implementation above
// uses process.nextTick).
//
// We use setImmediate here to give the stream enough time to emit all the
// events it's about to emit.
setImmediate(() => {
// Only the _read, push, readable calls have happened. No data must be
// emitted yet.
assert.deepStrictEqual(calls, ['_read:a', 'push:a', 'readable']);
// Calling 'r.read()' should trigger the data event.
assert.strictEqual(r.read(), 'a');
assert.deepStrictEqual(
calls,
['_read:a', 'push:a', 'readable', 'data:a']);
// The next 'read()' will return null because hwm: 0 does not buffer any
// data and the _read implementation above does the push() asynchronously.
//
// Note: This 'null' signals "no data available". It isn't the end-of-stream
// null value as the stream doesn't know yet that it is about to reach the
// end.
//
// Using setImmediate again to give the stream enough time to emit all the
// events it wants to emit.
assert.strictEqual(r.read(), null);
setImmediate(() => {
// There's a new 'readable' event after the data has been pushed.
// The 'end' event will be emitted only after a 'read()'.
//
// This is somewhat special for the case where the '_read' implementation
// calls 'push' asynchronously. If 'push' was synchronous, the 'end' event
// would be emitted here _before_ we call read().
assert.deepStrictEqual(
calls,
['_read:a', 'push:a', 'readable', 'data:a',
'_read:null', 'push:null', 'readable']);
assert.strictEqual(r.read(), null);
// While it isn't really specified whether the 'end' event should happen
// synchronously with read() or not, we'll assert the current behavior
// ('end' event happening on the next tick after read()) so any changes
// to it are noted and acknowledged in the future.
assert.deepStrictEqual(
calls,
['_read:a', 'push:a', 'readable', 'data:a',
'_read:null', 'push:null', 'readable']);
process.nextTick(() => {
assert.deepStrictEqual(
calls,
['_read:a', 'push:a', 'readable', 'data:a',
'_read:null', 'push:null', 'readable', 'end']);
});
});
});
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